Psilotum
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 Closeup of Psilotum nudum
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Psilotum (whisk fern) is a genus of fern-like vascular plants, one of two genera in the family Psilotaceae, order Psilotales, and class Psilotopsida (the other being Tmesipteris).
They had traditionally been thought not to be true ferns, but rather, odd "primitive" vascular plants similar to the fossil rhyniophytes and psilophytes. In addition, they lack true leaves and roots (like the Bryophytes), and thus represent the simplest of vascular plants, albeit whose "simple" features are the apparent reduction from more complex evolutionary predecessor. They do however have stems and rhizoids. Indeed, recent molecular genetic evidence (Qiu and Palmer 1999) has supported morphological evidence that they may in fact be ferns (Phylum Pterophyta) that have lost a number of pteridophytic characteristics.
There are two species, Psilotum nudum and Psilotum complanatum, with a hybrid between them known, Psilotum × intermedium W. H. Wagner.
The distribution of Psilotum is tropical and subtropical, in the New World, Asia, and the Pacific. The highest latitudes known are in South Carolina and southern Japan for P. nudum. In the U.S., one species is found from Florida to Texas, the other in Hawaii.
[edit] References
- Qiu, Y-L and Palmer, J (1999) "Phylogeny of early land plants: insights from genes and genomes." Trends in Plant Science 4(1), 26-30
